(i) Field of the Invention
The present invention relates to a glass-ceramic composition for use, for example, in a circuit substrate or a chip component, a circuit substrate using the composition and a method of manufacturing the circuit substrate.
(ii) Description of the Related Art
Recently, in response to request for higher performance of ceramic substrates and miniaturization of chip components, a glass ceramic substrate has been turned to practical use Detail compositions, manufacture methods, and the like are described in Japanese Patent Publication Nos. 97565/1994 and 69902/1994.
For example, Japanese Patent Publication No. 97565/1994 discloses a glass ceramic composition in Example 1, in which a weight ratio of glass and Al.sub.2 O.sub.3 is 66:34 (33.5 wt %: 17.1 wt %). The glass is composed of 17.2 wt % of PbO, 4.5 wt % of B.sub.2 O.sub.3, 56.5 wt % of SiO.sub.2, 9.1 wt % of Al.sub.2 O.sub.3, 8.6 wt % of CaO, 2.4 wt % of Na.sub.2 O, and 1.7 wt % of K.sub.2 O. A glass deformation temperature is 590.degree. C., a softening point is 660.degree. C., and a difference of the softening point and deformation temperature is 70.degree. C. It is further described that a glass ceramic tape obtained by sintering the glass-ceramic composition is superior in dimensional stability.
Moreover, Japanese Patent Publication No. 69902/1994 discloses a glass ceramic composition in Example 1, which is composed of 60 wt % of glass and 40 wt % of Al.sub.2 O.sub.3 The glass is composed of 50 wt % of SiO.sub.2, 6 wt % of Al.sub.2 O.sub.3, 35 wt % of PbO, 5 wt % of (MgO+CaO+SrO+BaO), 1 wt % of ZnO, 0.5 wt % of B.sub.2 O.sub.3, 0 wt % of (Li.sub.2 O+Na.sub.2 O+K.sub.2 O), and 2.5 wt % of (TiO.sub.2 +ZrO.sub.2). It is described that when the composition is formed into a slurry and a resulting green sheet is fired, an obtained substrate has large resistance strength and large thermal conductivity, and is superior in thermal resistance and chemical resistance. It is further described that when Ag--Pd conductors are formed on the green sheet by screen printing, laminated and fired to form a glass-ceramic laminate, a multilayered circuit element is superior in solder wettability and bonding strength.
These glass-ceramic compositions or the glass-ceramic composites have been heretofore used as circuit substrates by forming conductor paths inside or on the surface of the each layer or the laminate. However, matching properties with various conductor materials have not been studied sufficiently.
The present inventors have studied this respect, and found out the following problems. Specifically, in the case where a glass composition having a high softening point is employed, when an Ag or Au system conductor circuit is screen-printed on the green sheet and then fired, conductor materials are dispersed in a ceramic, thereby deteriorating an insulating resistance, dielectric constant and other electric properties of the ceramic. A performance could not be obtained as designed. Moreover, in the case where a glass composition having a low softening point is employed, since the Ag or Au system conductor material is not sufficiently sintered, a bonding strength of the glass-ceramic composite and conductor circuit probably becomes insufficient. One of problems is the warp, or deformation of the substrate when the substrate is fired together with the conductive materials. For example, in a substrate in which a large number of pieces each of about 1.times.10 mm are arranged on a large plate with a size of about 100.times.100 mm, the generation of the warp, or deformation causes a fatal defect in a solder printing process after the substrate is fired, or in a process for mounting electronic components or parts.